In a video system that uses a positive composite video signal, there is needed a burst gate pulse which is used in a video phase locked loop (PLL) block, as well as some reference synchronizing signals such as horizontal, vertical and composite synchronizing signals. Therefore, the PLL system requires a local oscillator having its oscillation frequency of 3.58 MHz (In other systems, it may be divided in frequency from 14.32 MHz) which is used as a reference signal for color signals in a receiver of the video system. To assure coincidence of a phase of the oscillation frequency with a burst signal of the input composite video signal, it requires a pulse signal to inform a position of the burst signal. The pulse signal is referred to as the burst gate pulse signal.
The video system of prior art has been equipped with an exterior synchronizing circuit which adopts discrete and operational amplifiers, wherein the phase is made to coincide with the burst signal of the input composite video signal in generating a signal having a frequency and a duty rate which is the same as that of the burst. Because the exterior circuit consists of several components, it raises the cost in producing the system. Moreover, it becomes very difficult to make the phase coincide with the burst signal of the input composite video signal if another synchronizing circuit is not equipped therewith, and thus the quality of the burst gate pulse began to degrade.